The overall goal of this Program is to define approaches to oligonucleotide-based modulation of gene expression and the mechanistic bases of their effects. The Program contains four Projects and two Cores. Each Project will investigate in a critical manner a distinct aspect of this therapeutic approach. Project 1. (Project Director: Stephen Liebhaber) focuses on an analysis of nucleic acid decoys which target RNA-protein complexes critical to mRNA stability. This project integrates in vitro, cell culture-based, and transgenic studies to define the critical parameters in expressing functional RNA decoys and in evaluating their level of specificity and mechanisms of action. Project 2 (Project Director: Kazuko Nishikura) focuses on the role of double-stranded RNA adenosine deaminase activity (DRADA) to modify RNA double-strand regions formed by antisense oligonucleotide interaction with mRNA. This work is based on Dr. Nishikura's pioneering studies identifying and characterizing this novel RNA editing activity. Project 3 (Project Director: James Eberwine) deals with the specificity and mechanisms of action of antisense sequences in neuronal cells. This work is based on the unique methodologic approaches which have been developed in his laboratory to define mRNA profiles in live single-neuron preparations. The fourth project (Project Director: Anan Gewirtz) carries out an indepth analysis of the effects of antisense oligonucleotides on the expression of the Vav protooncogene. This study exemplified a critical translatiional component of this Program designed to validate and evaluate the mechanisms and specificity of the antisense therapeutics. Dr. Gewirtz has substantial experience in the clinical applications of antisense oligonucleotides and is a leader in the development of this therapeutic modality. The two Cores (Administrative andNucleic Acid Synthesis) support the efforts of each of the four Projects. Each of the Project Directors is an established investigator with a substantial interest in the biology or RNA and the effects of mRNA structure on its expression. The areas of expertise of each of these investigators is non-overlapping and complimentary. This combination should result in a synergy of total efforts. The distribution of basic mechanistic studies, novel approaches, and therapeutic applications combine to result in a long-range goal of establishing a firm biochemical basis for the applicaiton of oligonucleotide-based therapeutics to a broad range of clinical problems reflecting obnormalities in gene expression.